a white house official says the obama administration is handling an attack at the boston marathon as an act of terror. two bombs went off just before the finish line. at least three people were killed. one of them was an 8-year-old boy. more than 100 others were wounded. the first bomb knocked back runners 30 meters from the finish. then another explosion hit people a short distance away. emergency services rushed to the scene. there was no word on the motive or on who may have been responsible. investigators are working to find out whether the attack was carried out by a terrorist group from inside or outside the country. the explosions have revived memories of the september 11th terror attacks. authorities have tightened security in cities around the country, and they may review measures to keep americans safe. nhk world's reporter has more. >> reporter: this was the 117th running of the boston marathon. the world's oldest annual sporting event. more than 23,000 runners took part. several recounted the horror. >> i literally saw the garbage garl explode. i saw the flash, the fire a